150 g soft butter
150 g of sugar
150 g flour
1 tablespoon baking powder
4 egg whites
1 cup ground walnuts
For the topping:
4 egg yolks
1 cup of icing sugar
½ coffeespoon natural vanilla extract
Cream the butter and sugar in a deep bowl. Add the baking powder, flour and walnuts. Mix well.
Whisk the egg whites until stiff peeks with a pinch of salt. Gently stir into the mixture above. Pour the batter into a square mold, greased and floured. Bake about 20-30 minutes at 180°C. Leave aside to cool completely.
In another bowl, stir the egg yolks, sugar and vanilla. Stir very well until smooth and creamy. Top the cake with this cream and leave one night at room temperature to dry. If you do not have that much time, you could dry it in the oven, at low temperature. At about 50°C for 5 to 10 minutes.
When reay to serve, cut square pieces with a warm knife (otherwise the topping will crack up.